This invention relates generally to a clearance measuring method and apparatus, and more particularly, to a method and apparatus for measuring the clearance between a rotating member and a stationary member of a turbine or the like.
In order to assure proper performance of a turbine, such as a jet engine, it is important to establish proper clearance between the blades which form part of the rotating member of the turbine and the stationary member which encloses the rotating member to form an assembled combination. This clearance is generally established by measuring the clearance between these elements after their assembly, but prior to initial operation of the turbine (the cold clearance measurement). If this cold clearance measurement changes, or is not statisfactory, a proper running tip clearance will not be established and proper operation of the turbine will now be obtained.
To perform such a cold clearance measurement, the following steps are presently necessary. First, the rotor must be assembled by attaching the blades to the core of the rotor in the conventional manner. During this operation, at least one of the blades is fitted with a measuring device which will be used in obtaining the cold clearance measurement. The rotor (and blades) is then located within the casing so that the blades are located in the position which they will assume when the turbine is to be operated. At this time, after such a unit has been at least partially assembled, the clearance between the blades of the rotor and the inner wall of the casing is measured by appropriately monitoring the measuring device previously attached to one of the blades and by rotating the rotor through one or several rotations. After this alignment procedure is completed, it becomes necessary to remove the measuring device from within the assembled unit prior to initial operation of the turbine, since operation of a turbine which contains such a measuring device could seriously damage components of the turbine. To remove the measuring device from the assembled unit, it is necessary to completely disassemble the unit and detach the measuring device from the blade (or blades) to which it is attached. The unit is then reassembled, taking care not to change the alignment between the various components comprising the unit, so that the previously performed clearance measurement is not altered.
Although this method has proved satisfactory in obtaining a proper running tip clearance, this method presents several serious drawbacks, primarily due to the fact that after the cold clearance measurement is made it becomes necessary to completely disassemble the aligned unit to remove the measuring device used. This is an extremely time consuming procedure, involving substantial hours of highly skilled labor, in order to assure that the reassembled unit maintains the same clearance measurement as obtained initially. Moreover, since it is extremely important that the components of the unit be unchanged when reassembled, to maintain the original cold clearance measurement, a significant potential for error, and accordingly damage, is introduced into the assembly procedure.
Apparently recognizing these problems, a variety of devices and techniques have been developed which attempt to more easily measure such clearances, without having to disassemble components after such clearance measurements have been obtained. However, none of these devices or techniques also provide a means for obtaining a complete and continuous measurement of the distance between the rotating member and the inner wall of the stationary member, as has been found to be desirable in such applications.
It is therefore desirable to provide a method and apparatus for properly measuring the clearance between a rotating member and a stationary member of an assembled, or partially assembled turbine in a continuous and accurate manner, without requiring disassembly or alteration of turbine components after this clearance is established.